Frog-eating bats remember ringtone years after training

Frog-eating bats trained by scientists to associate a phone ringtone with a tasty treat could surprisingly remember what they learned after up to four years in the wild, a new study has revealed.

In the research published in the journal Current Biology on Monday, scientists acquainted 49 bats with a series of ringtones that attracted their attention, and trained them to associate flying toward just one of the tones with a reward – a baitfish snack.

They recaptured eight of the bats and exposed them again to the food-related ringtone between one and four years later.

All the bats flew toward the sound, and six flew all the way to the speaker and grabbed the food reward, scientists say, suggesting the bats expected to find food.

“I was surprised – I went into this thinking that at least a year would be a reasonable time for them to remember, given all the other things they need to know and given that long-term memory does have real costs,” study lead author May Dixon from the Ohio State University said in a statement.

“Four years strikes me as a long time to hold on to a sound that you might never hear again,” Dr Dixon said.

In the first phase of the study, individual frog-eating bats captured for a series of cognition tests were exposed to a highly attractive sound in the lab. These included the mating call of the male túngara frog, one of this species of bats’ preferred prey.

When bats flew to this sound, they were rewarded with a piece of baitfish placed on mesh above the speaker.

Researchers then mingled the sound and gradually replaced it by a ringtone, but the reward was the same.

They also introduced three other ringtones, none of which were connected to a food reward.

Scientists trained the bats to discern the differences between the ringtones, and they eventually no longer flew toward the unrewarded sounds.

Each bat, according to the study, secured at least 40 snacks by flying to the trained ringtone over 11 to 27 days, and all of them were microchipped and returned to the wild.

Researchers then recaptured them and identified eight of the bats from the initial trial by their microchips.

In a follow up test, they found that all eight trained bats quickly flew to the sound and were able to tell the difference between that ringtone and a new, steady tone, though many did fly to an unrewarded sound from the initial training.

In comparison, scientists say that 17 untrained bats that were exposed to these sounds mostly just twitched their ears in response to the sounds and did not fly toward them.

“The study taught us a lot because there are relatively few studies of long-term memory in wild animals and we don’t have systematic understanding of long-term memories in nature yet,” Dr Dixon said.

“If we can collect additional data on different species of bats, we could pick this apart and see what life histories select for long memories.”

While several studies in the past have documented memory in species ranging from fish, birds and bats to goats and primates, with some such as sea lions demonstrating long-term memory for 10 years, researchers say these were mostly conducted on animals that lived in captivity the entire time.

“Being able to study memory in the wild is important,” Gerald Carter, another co-author of the study, said.

“You can’t necessarily extrapolate from the wealth of data we have on animals in the lab to what they’re facing in the wild, where there are many more things they have to remember. The environment is different and the brain is different in the wild versus captivity,” Dr Carter explained.

Although long-term memory gives humans an intelligence advantage, scientists say memory flexibility – also called adaptive forgetting – may be important for survival.

“It’s not always true that being the smartest or having the longest memory is actually advantageous. Research has shown that fruitflies selected for improved memories can’t compete as well against other fruitflies,” Dr Dixon said.

“Just because it’s useful for humans to be so smart and have such good memories doesn’t necessarily mean it’s going to be the best thing for other animals,” she added.

In further studies, scientists hope to understand when these memory skills are actually helping animals and when they could be a liability.